In recent years, flame-retardant products are used in a wide range of applications, including automobile parts, home electric appliances, construction materials and parts of vehicles. In particular, molded products such as appliance wiring, cables, electric cords, plugs and sheets are required to have flexibility and high flame retardancy to ensure operability and utility.
Conventional flame-retardant compositions containing vinyl chloride resins that meet these requirements are still in use in the above-described applications. However, conventional flame-retardant composition containing vinyl chloride resins produce toxic gases that can corrode skin and mucous membranes when burnt or exposed to flame or high temperatures. If inhaled, these gases may cause suffocation, loss of consciousness or even death depending on their concentration. In addition, vinyl chloride resins contain plasticizers, such as DEHP, that disrupt endocrine function. For these reasons, there is a great need for a substitute material for these resins.
To meet this need, halogen-free flame-retardant compositions have been proposed, each of which includes a metal hydrate dispersed in a thermoplastic resin and does not produce corrosive toxic gases when burnt. In particular, flame-retardant compositions including a metal hydrate mixed in a polyethylene or polyethylene copolymer are used in commercial products known as “eco-wires” in the market of electric wire products. However, it has been pointed out that these compositions, because of containing the metal hydrates in large amounts, have problems in flexibility, processability and productivity of the products.
Many products have been proposed to eliminate these problems. Examples thereof include products using a polyolefin resin that is crystallized in a controlled manner (Patent Document 1); products including a polyolefin resin and an elastomer, such as styrene thermoplastic elastomer (Patent Documents 2 and 3); products including a polyolefin resin and a styrene thermoplastic elastomer modified with functional groups (Patent Document 4); and dynamic crosslinked products including a polyolefin resin, a styrene thermoplastic elastomer and a non-aromatic rubber softener (Patent Documents 5 and 6). Aside from resins, many flame-retardants and flame-retardant assistants have also been proposed. Nonetheless, each of these flame-retardant compositions has its own drawbacks. Some fail to provide sufficient improvements, some tend to lose strength and heat resistance, some tend to be decomposed due to required high kneading temperatures, and some require complicated production processes. Thus, no flame-retardant compositions of satisfactory properties have been not available.    Patent Document 1: Japanese Patent Application Laid-Open No. H10-95876    Patent Document 2: Japanese Patent Application Laid-Open No. H2-145633    Patent Document 3: Japanese Patent Application Laid-Open No. 2002-179878    Patent Document 4: Japanese Patent Application Laid-Open No. Hei 2-53846    Patent Document 5: Japanese Patent Application Laid-Open No. 2000-143935    Patent Document 6: Japanese Patent Application Laid-Open No. 2003-128849